Patent GB-649287-A (GB)
Title: Improvements relating to fuel systems for gas-turbine engines
Inventor: DAVIES KENNETH ROY
IPC: F02C7/22
Filed: 1948-04-22
Abstract: 649,287. Gas turbine plant fuel systems. ROLLS-ROYCE, Ltd. April 22, 1948, No. 11059. [Class 110(iii)] [Also in Group XXIX] A gas turbine engine fuel system comprises a fuel pump for delivering fuel to the engine and control means for the fuel flow which includes two hydraulic governor means, one of which defines in acceleration for each instantaneous rotational speed of the engine a maximum fuel supply to the engine which is in excess of the engine requirements at that speed and the other, which has a variable datum by which a desired steady running rotation speed may be selected, controls the fuel supply so as to determine and maintain such desired speeds. A hydraulic governor means is defined as a pressure responsive device for varying the fuel flow arranged to be responsive to the pressure drop across restricting means through which a fluid is caused to flow by a fixed volumetric capacity pump driven at a speed proportional to the engine rotational speed. Both of the hydraulic governors may have a common restricting means and the fuel pump may also be the fixed volumetric capacity pump. The burners 21 of a gas turbine plant are supplied with fuel from a tank 16 by variable capacity reciprocating multi-plunger pump 10 through a pipe 17, a slide valve 34, chamber 36, a second valve 42 and pipe 39. The stroke of the pump 10 is controlled by the pressure in the pipes 39 and 17. An engine driven fixed volumetric capacity pump 22 passes fuel through a circuit, including a fixed metering orifice 25, pipe 26 and return pipe 27. The pressure drop across the orifice 25 is applied to the pressure responsive diaphragms 29 and 43 of the hydraulic governors. The diaphragm 29 operates the slide valve 34 controlling the fuel supply to the chamber 36 and is opposed by the pressure drop across the diaphragm 37 which is open on one side to the chamber 36 and on the other to the discharge pipe 39. As the pressure drop across the second valve 42 is proportional to the square of the engine rotational speed, the valve 34 will control the pressure in the chamber 36 so that the pressure drop across the second valve 42 is also subtantially proportional to the square of the engine speed. The second valve 42 can be moved in two senses and is arranged to be rotated by the action of the diaphragm 43 and to be moved axially by an altitude capsule 58. The diaphragm 43 is loaded by a spring 47 the load of which can be varied by a power control lever 48 as well as by the pressure drop across the orifice 25. Movements of the diaphragm 43 rotate a shaft 51 which carries a crosshead 52 engaging in axial slots 53 formed in the slide valve 42. A spring 54 urges the valve 42 axially to the right, whilst movement to the left is effected by a servometer piston 55. This piston has a passage 56 the flow through which is controlled by a plunger 57 connected to the altitude capsule 58. Reduction of the atmospheric pressure causes the capsule 58 to expand, the plunger 57 to close the passage 56 and the pressure in the chamber 61 to rise. This action results in movement of the piston 55 to the left against the spring 54 and the valve 42 to close the port 67. Upward movement of the diaphragm 43 also causes the valve 42 to close the port 67. To vary the load on the engine, the lever 48 is moved so as to compress or relieve the load on the diaphragm 43 caused by the spring 47, which diaphragm then moves to open or close port 67. The amount of opening or closing of the port 67 by the valve 42 is limited by adjustable stops so that the maximum and minimum fuel supply can be adjusted and be dependent only on the pressure drop across the port which is proportional to the engine speed and controlled by the diaphragm 29. The capsule 58 will vary the maximum and minimum fuel supply in accordance with changes in altitude. In a modification, the variable capacity fuel pump 10 is replaced by a fixed volumetric capacity pump which pumps the fuel through a variable area orifice and a fixed orifice arranged in series in the pipe line 17. The pressure drop across the fixed orifice is applied to the diaphragm 29 and the pressure drop across the variable area orifice is transmitted to the opposite sides of a spring-loaded piston which is used to control rotational movement of the shaft 51 in place of the diaphragm 43. The member varying the area of the orifice is connected to the control lever 48 and performs the function of the spring 47. Excess fuel is byepassed back to the fuel tank from the pipe 17 through a spring-loaded byepass valve which is also loaded by the pressure in the pipe 39. In a modification of the latter system, the fixed orifice is replaced by a variable area orifice the effective area of which is controlled by a capsule which is responsive to the atmospheric temperature. In this arrangement, the first mentioned variable area orifice is also provided with a spring-loaded byepass valve, which opens when the pressure drop across the orifice exceeds a predetermined value. This prevents excessive cut off of the fuel to the engine on rapid deceleration. It is also stated that the use of a variable area orifice controlled by the lever 48 may be used to control the movements of the diaphragm 43 alone or in conjunction with the variable loading of the spring 47. If desired, a temperature sensitive element in the exhaust duct of the engine may be used to control a byepass valve in the pipe 39 to apply a load to the capsule 58, the load imposed on the plant or to modify the restricting orifice 25 in the event of an excessive rise of temperature. Specification 604,466 is referred to.